Butterfly valves are one of many types of valves that are used to control the flow of fluids. A conventional butterfly valve includes a disc (also called a butterfly), that is rotated within a housing bore or passage to block fluid flow in varying amounts. Typically, the disc is mounted to turn on an axis that traverses the housing bore or passage so that the disc can rotate between an open position and a closed position. When the disc is in the open position, the plane of the disc is generally coincident or parallel to the direction of flow and the fluid flow rate is maximized. When the disc is in the closed position, the plane of the disc is transverse/orthogonal to the direction of flow and the fluid flow rate is minimized or completely stopped.
Conventional butterfly valves further include a fluid seal that is provided, for example, by the outer edge of the disc or by a sealing member, such as, for example, one or more butterfly rings, that is/are attached to the outer edge of the disc. The fluid seal can engage with the interior of a valve housing or with a seating surface on the interior of a housing or passage to provide fluid sealing when the butterfly is rotated to the closed position.
Butterfly rings are typically contained in a groove around the outer periphery of the butterfly disc. The rings are typically flat and have a circular shape. The rings can include a split to accommodate compression and/or expansion in diameter of the ring.
Rings are typically employed to accommodate surface irregularities and manufacturing tolerances of the butterfly, minimizing inherent leakage that can occur between the butterfly and the housing or passage in which the butterfly is placed. It is often desirable for the rings to be as close to centered in the housing or passage in which the butterfly is positioned as possible. However, using high precision machining and manufacturing to place the rings in the exact center of a bore is not practical. Therefore, conventional rings are typically permitted to float on the butterfly so that the rings can “find” the center of the bore when the butterfly is closed, even though the butterfly may be off center within the bore. In this manner, the rings are centered through contact between the outside edge of the rings and the bore of the housing or passage.
In conventional butterfly valves, the rings expand to the diameter of the housing or passage bore during actuation of the butterfly. In this manner, the rings function as resilient components that accommodate the surface irregularities and manufacturing size tolerances of the butterfly. In conventional butterfly valves, the rings seal the butterfly valve through contact between the outer edges of the rings and the bore of the housing or passage, and seals by contact between the face of the rings and the butterfly (e.g. a groove in the butterfly may be present to accept the rings, allowing the rings to spring outward while still being retained in the groove).
Rings in conventional butterfly valves can function as springs to keep the rings in intimate contact with the bore when the butterfly is in a closed position (the spring effect resulting in the resilient features of the rings). In some designs, these rings can be forced radially outwards by fluid pressure that acts within the butterfly groove between the butterfly disc and the inside edge of the ring or rings. When the fluid pressure is high, the force pressing the rings outward is high. In this way, the rings of conventional butterfly valves can be forced outwards by a combination of mechanical spring force and a fluid pressure force.